1. Field of the Invention
The present invention relates to an organic thin film transistor (TFT) and a flat panel display having the same, and more particularly, to an organic TFT that has a reduced contact resistance between source/drain electrodes and an organic semiconductor layer and a flat panel display having the same, and methods of manufacturing the organic thin film transistor and flat panel display device.
2. Description of the Related Technology
A conventional silicon thin film transistor (TFT) has a semiconductor layer. The semiconductor layer includes source and drain regions doped with a high concentration of dopant and a channel region formed between the source region and the drain region. The TFT also includes a gate electrode disposed on a region overlapping with the channel region. The gate electrode is insulated from the semiconductor layer. The TFT further includes a source electrode and a drain electrode respectively connected to the source region and the drain region.
However, conventional silicon TFTs have high manufacturing costs, and are easily breakable by an external impact. In addition, the TFTs cannot use a plastic substrate since the silicon TFT is produced at a temperature greater than about 300° C. The TFTs may be used either as a switching device or as a driving device for each of the pixels in flat panel display devices, such as a liquid crystal displays (LCD) and electroluminescence displays (ELD).
To provide flexible panel display devices having a large screen size and a thin thickness, attempts have been made to use plastic materials for forming a substrate instead of a conventional glass material. However, a low temperature process must be employed to process the plastic materials. Therefore, conventional silicon TFTs, which are processed at a high temperature, cannot employ plastic substrates.
On the other hand, this problem can be solved when an organic film is used as a semiconductor layer of a TFT. Therefore, studies about organic TFTs that use an organic film as a semiconductor layer have been actively performed. For example, poly-acetylene is a conjugated organic polymer that has semiconductor characteristics. It can be synthesized in various ways at a low cost, and can be easily molded in a fabric or film shape. Poly-acetylene also has flexibility and conductivity required for use in organic material-based transistors.
However, there is high contact resistance between source and drain electrodes and the organic film when an organic TFT is used as a semiconductor layer. That is, a high concentration of dopant cannot be implanted in the organic semiconductor layer included in the organic TFT unlike the silicon semiconductor layer included in the conventional silicon TFT. Accordingly, an ohmic contact cannot be formed between the source and drain electrodes and the organic semiconductor layer due to high resistance therebetween.